1. Field of the Invention
The present invention relates to an imaging lens and an imaging apparatus, more particularly, to an imaging lens suitable to be used in a surveillance camera, a cell phone camera, an onboard camera, and the like employing an imaging device such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor), and an imaging apparatus having the imaging lens.
2. Description of Related Art
Recently, imaging devices such as CCD and CMOS have been excessively downsized and the number of pixels of those has been excessively increased. In addition, an imaging apparatus main body having the imaging device has been also downsized, and thus it is also required to unweight and downsize an imaging lens mounted therein.
Meanwhile, in an onboard camera, a surveillance camera, and the like, there is required a small-sized and high-performance lens that has high antiweatherability in the range from outside air in a cold region to a vehicle inside in summer of a tropical region and can be used in the wide temperature range. Particularly, in the camera disposed in a vehicle to observe the front side thereof, there is required a lens usable in the wide wavelength range from the visible band to the infrared band. In addition, in case of the onboard camera, there is also required a lens of which only a small part is exposed to the outside in consideration of an exterior view of a vehicle.
In JP-A-2006-64829, JP-A-2006-91715 and JP-A-2006-91718, as a lens usable in the wide wavelength range from the visible band to the near-infrared band, there was disclosed a telephoto lens system having a four group configuration that includes, in order from the object side, a first lens group having a positive power, a second lens group having a positive or negative power, a third lens group having a negative power, and a fourth lens group having a positive power. In the lens system disclosed in JP-A-2006-64829, JP-A-2006-91715 and JP-A-2006-91718, a lens closest to the object side in the second lens group has a convex surface on the object side, and an aperture diaphragm is disposed between the third lens group and the fourth lens group.
However, in JP-A-2006-64829, JP-A-2006-91715 and JP-A-2006-91718, the aperture diaphragm is disposed closer to the image side than the third lens group. Since the aperture diaphragm is located close to the image plane, a light ray height in the lens closest to the object side increases. Thus, there is a disadvantage that a diameter of the lens becomes large. Particularly, in the onboard camera, it is preferred that an exposed area of the lens surface be small in an exterior view, and so it is preferred that a diameter of the lens be small.